Aberrant polyadenylation by a vesicular stomatitis virus mutant is due to an altered L protein

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Abstract
TsG16(I) is a temperature-sensitive mutant of vesicular stomatitis virus, Indiana serotype. Our stocks of this mutant overproduce polyadenylic acid in an in vitro transcription system. The overproduction of polyadenylic acid occurs at all temperatures tested (27, 31, 35, and 39 degrees C) and is apparently not due to an alternation in the N protein-RNA template. To characterize the altered moiety in tsG16(I) responsible for this phenotype, virions were fractionated and the polyadenylation phenotype in homologous and heterologous reconstitution assays was determined. The aberrant polyadenylation phenotype correlated with the presence of ts L protein but not ts NS or ts M protein fractions. Results of experiments in which solubilized tsG16(I) and wild-type virion components were mixed indicated that the altered moiety behaved as if present in stoichiometric amounts relative to active L protein. The effects of raising the temperature from 31 to 39 degrees C in such mixes were as would be predicted upon the assumption that the polyadenylation phenotype was associated with a thermosensitive transcriptase component [the L protein of tsG16(I) is known to be thermosensitive]. We conclude that the data strongly support the hypothesis that L is the altered protein responsible for the aberrant polyadenylation phenotype of tsG16(I).